Since we know about vibration and its types in our previous blog , now next question comes in our mind is how to measure it?

 

 

Frequency

Vibrating object moving from one extreme position to other extreme and back again; equals to one cycle (refer figure 1). Number of cycles completed in one second is known as frequency. Using frequency, we can pin point the vibration source that from where it is coming from.

Measuring Unit: Hertz (Hz) or CPS (Cycle per Second) or CPM (cycle per minute) or RPM (Rotation per minute)

      1 Hz = 1 CPS = 60 CPM = 60 RPM

Amplitude

Maximum distance travelled by a vibrating object, represents amplitude(refer figure 1). In vibration field, amplitude is a key component which tells about severity or intensity of vibration.

It can be measured in three forms: Displacement, Velocity & acceleration(refer figure 2).

  • Displacement: Maximum distance traveled by object i.e. peak to peak.

Measuring Unit:Mils or Microns

  • Velocity: Rate of change of displacement or the speed at which object vibrates. Practically the on-site vibration time waveform is not always sinusoidal but have noise disturbances so to eliminate that we are taking RMS value instead of peak, this will reduce the fluctuation in our readings and easy to monitor vibration trend.

Measuring Unit: inch/s or mm/s

  • Acceleration: Rate of change of velocity with time or second derivative of displacement with time. It can be measured zero to peak or peak to peak; depends on analyst.

Measuring Unit: m/s² or g (acceleration due to gravity i.e. 1g = 9.8 m/s²)

Phase

The relationship between two signals vibrating at same frequency. It helps vibration analyst to confirm the problem in vibrating sources. Relation ship of phase between displacement, velocity & acceleration shown in figure 3.

 

Measurement Unit:Degree (˚)

 

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